1. Field of the Invention
This invention relates to a reflective liquid crystal display device, more particularly to a reflective liquid crystal display device having an auxiliary light source.
2. Description of Related Art
In general, liquid crystal displays are divided into transmissive liquid crystal display devices and reflective liquid crystal display devices according to whether the display uses an internal or outer light source.
While the transmissive liquid crystal display device uses an internal light source such as a backlight, the reflective liquid crystal display device uses ambient light and thus is affected by its surroundings. For example, the brightness of ambient light in an office differs largely from that outdoors. Also, even in the same location, the brightness of ambient light depends on the time of day (e.g., noon or dusk). An auxiliary light source device for the reflective liquid crystal display device is mainly used when its surroundings get dark.
FIG. 1 shows an auxiliary light source device for the reflective liquid crystal display device which has a light-directing member. The auxiliary light source device includes a light source 63, a lamp reflector 65 and a light-directing member 67. The auxiliary light source device is mounted on a liquid crystal display panel 61 having a reflector 71.
The light source 63 is located adjacent to an end 67a of the light-directing member 67, and most of the light source 63 is surrounded by the lamp reflector 65. The end 67a constitutes a surface through which the incident light from the light source 63 is emitted. The light-directing member 67 also has upper and lower surfaces 67b and 67c. A wall-reflector 69 is mounted along the side walls of the light-directing member 67 other than the emitting surface 67a in order to direct the incident light the incident light from the light source 63 is emitted. The light-directing member 67 also has upper and lower surfaces 67b and 67c. A wall-reflector 69 is mounted along the side walls of the light-directing member 67 other than the emitting surface 67a in order to direct the incident light toward the liquid crystal display panel 61 disposed under the light-directing member 67.
The emitted light from the light source 63 is directed toward the surface 67a of the light-directing member 67 and to the inside of the light-directing member 67 by the lamp reflector 65. The light-directing member 67 directs the incident light toward the liquid crystal display panel 61. The light transmitted to the liquid crystal display panel 61 is reflected by the reflector 71 and is emitted toward the observer 73.
It should be noted that the auxiliary light source device is mounted on the liquid crystal display panel. Thus, there cannot be a diffusion plate and lens sheet between the liquid crystal display panel and the light-directing member, unlike in a transmissive liquid crystal display device. In order to produce a uniform emitted light distribution, the following four conditions are preferred for the auxiliary light source device of the reflective liquid crystal display device.
First, an incident light from the light source should be directed only toward the liquid crystal display panel and not the observer. Second, the incident light from the light source should be emitted perpendicular to the liquid crystal display panel. Third, the incident light from the light source should be distributed uniformly toward the liquid crystal display panel by the light-directing member. Fourth, the auxiliary light source device should be designed to minimize undesired effects such as a surface reflection and an angle distortion of the incident light from the auxiliary light source by the light-directing member.
Surface light source devices that have a diffusing plate and a lens sheet to increase the brightness are disclosed in U.S. Pat. Nos. 5,584,556 and 5,575,549. But these devices are used for the transmissive liquid crystal display, and the diffusion plate and the lens sheet disposed between the liquid crystal panel and the light-directing member, as explained previously, are not suitable for the reflective liquid crystal display device.